The present invention relates generally to turbine engines, and more particularly, to an axial entry integrally shrouded turbine bucket closure assembly.
In at least some known turbine engines, such as gas turbines and steam turbines, axial entry buckets, i.e., rotor blades, are coupled to a rotor wheel by sliding the buckets generally parallel to the rotor axis and into mating dovetails formed on the rotor wheel. Some known buckets include radially-inwardly projecting dovetails that mate in dovetails on the rotor wheel. The rotor wheel dovetails are circumferentially spaced apart from each other about the periphery of the rotor wheel.
Some known turbines, however, use integral covers or shrouds along the bucket tips. Generally, the shrouds have overlapping protrusions that nest with the shrouds of adjacent buckets. Some known shrouds may have a Z-shaped configuration when viewed in a radially-inward direction. As the buckets are assembled around the rotor wheel using the axial entry dovetail system, the shrouds of the first and the next to the last assembled buckets may prevent assembly of the final axial entry bucket. The blocking portions of the shrouds cannot be removed because the shrouds are designed to fit tightly together and in contact with each other to maintain a continuous circumferential coupling of the buckets at their tips. As a result, the clearance between the shrouds on the buckets adjacent to the closure bucket location is insufficient to permit axial insertion of the closure bucket.
To facilitate insertion of the final axial entry bucket, at least some known turbines use a dovetail closure insert to secure the closure bucket. However, using a dovetail closure insert increases the cost of such known turbines and may also increase operating stresses induced in the bucket to the rotor wheel assembly. As such, known methods of securing the final or closure bucket with its shroud to the otherwise completed rotor wheel assembly by the axial entry assembly method may be difficult and time-consuming, and may increase operating stresses on the turbine.